If we can violate the original premise lf "three- and four-letter words," I offer

least
slate
stale
steal
tales
taels
teals
Tesla

and the more questionable
setal -- pertaining to bristles (setae)
Stael -- as in "Madame de"

I recall a TV audience-participation show from the Fifties wherein the contestant had to arrange a set of letters into a word, with a 0 behind all but one of the letters and a 1 behind that all-important one, the numbers then being uncovered to reveal how much money had been won in that round...

Also

Etons
notes
onset
steno
stone
tones
which has the added virtue of allowing any of the letters to be the Big One. 'Onest !